Prostasin is a trypsin-like serine protease that is present in a variety of mammalian tissues. It is a membrane anchored protease that is expressed on the extra-cellular membrane of cells but that can also be secreted into body fluids such as semen, urine and airway surface liquid. Prostasin (PRSS8), together with proteases such as matriptase, CAP2, CAP3, trypsin, PRSS22, TMPRSS11, cathepsin A, and neutrophil elastase, can stimulate the activity of the amiloride-sensitive epithelial sodium channel (ENaC). Inhibiting these enzymes can induce changes in epithelial ion transport and therefore fluid homeostasis across epithelial membranes. For example, CAP inhibition in the kidney is thought to promote diuresis, whilst CAP inhibition in the airways promotes the clearance of mucus and sputum in lung. CAP inhibition in the kidney may therefore be used therapeutically to treat hypertension. CAP inhibition in the airways prevents the stagnation of respiratory secretions that otherwise tends to make sufferers vulnerable to secondary bacterial infections.